Use of partial esters of oligoglycerols with fatty acids as pigment dispersants for water-based lacquer dispersions

ABSTRACT

The physical and chemical properties of a pigment-containing, water-based lacquer dispersion are improved by adding thereto a partial ester of an oligoglycerol obtained by condensation of 2 to 20 moles of glycerol with a C 2  -C 18  fatty acid. The partial ester may be ethoxylated and/or propoxylated, and the fatty acid may be hydroxy substituted.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to the use of optionally ethoxylated and/orpropoxylated partial esters of oligoglycerols obtainable by condensationof 2 to 20 glycerol molecules with optionally hydroxy-substituted C₂₋₁₈fatty acids as pigment dispersants for water-based lacquer dispersions.

Discussion of Related Art

Partial esters of oligoglycerols obtainable by condensation of 2 to 20glycerol molecules with fatty acids are known, cf. Fette, Seifen,Anstrichmittel, Vol. 88, pages 101 to 106 (1986); DE-C 25 11 807. Thesepartial esters are often used as internal lubricants and/or antistaticadditives for plastics.

Anionic dispersants are frequently used as pigment dispersants forwater-based lacquer dispersions, as are nonionic dispersants based onadducts of ethylene oxide and/or propylene oxide with compoundscontaining active hydrogen atoms, cf. H. Kittel (ed.), Lehrbuch derLacke und Beschichtungen, Vol. III, pp. 250 to 258, Verlag W. A. Colomb,Berlin (1976), or low molecular weight polyacrylic acid salts, cf. DE-A3,318,595.

However, the use of the known dispersants in water-based lacquerdispersions is attended by various disadvantages. More particularly,unwanted foaming occurs to an increased extent in the water-basedlacquer dispersions.

DESCRIPTION OF THE INVENTION

Other than in the operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients or reaction conditions usedherein are to be understood as modified in all instances by the term"about".

The present invention is based on the observation that theabove-mentioned optionally ethoxylated and/or propoxylated partialesters of oligoglycerols obtainable by condensation of 2 to 20 glycerolmolecules with optionally hydroxy-substituted C₂₋₁₈ fatty acids havelittle, if any, effect on the foaming behavior of the water-basedlacquer dispersions. In addition, the partial esters improve thestability of the water-based lacquer preparations in storage and havelittle effect on their viscosity behavior. Finally, the partial estershave an excellent wetting effect which is reflected in high gloss levelsof the dried lacquer films. Finally, there is a noticeable improvementin resistance to methyl ethyl ketone and in the mechanical properties,particularly in the case of water-based alkyd resin preparations, bycomparison with low molecular weight polyacrylic acid salts as pigmentdispersants. In addition, water-based lacquer preparations, particularlywhere they contain alkyd resins, perform as well as correspondingstate-of-the-art lacquers in the condensation and salt spray testing ofmetal plates coated with the lacquer dispersions.

The partial esters to be used in accordance with the invention areprepared from oligoglycerols--obtainable by condensation of 2 to 20glycerol molecules--as the alcohol component, oligoglycerols synthesizedformally from 3 to 10 and more particularly from 4 to 6 glycerolmolecules being preferred for the production of the partial esters.Technical grade mixtures of the oligoglycerols having the stated chainlengths may also be used. Oligoglycerols obtainable by other methods arealso suitable for the preparation of the partial esters, cf. theabove-cited literature reference in Fette, Seifen, Anstrichmittel(1986).

To prepare the partial esters to be used in accordance with theinvention, the oligoglycerols mentioned above are partly esterified withoptionally hydroxy-substituted C₂₋₁₈ fatty acids, the partial esterspreferably containing at least one and, more preferably, at least twofree hydroxyl groups in the oligoglycerol part. Suitable fatty acids arelinear or branched, more particularly linear, saturated or unsaturatedfatty acids containing 2 to 18 carbon atoms. Typical examples of suchfatty acids are acetic acid, propionic acid, valeric acid, caproic acid,caprylic acid, capric acid, lauric acid, myristic acid, paimitic acid,isopalmitic acid, stearic acid, isostearic acid, palmitoleic acid, oleicacid, ricinoleic acid, linoleic acid, linolenic acid and12-hydroxystearic acid. Dihydroxyfatty acids, such as dihydroxystearicacid, hydroxyalkoxy-substituted and hydroxy-hydroxyalkoxy-substitutedfatty acids are also suitable. Compounds such as these may be obtainedfrom epoxidized fats and oils in known manner by ring-opening with wateror monohydric and polyhydric alcohols, such as for example methanol,ethanol, ethylene glycol, glycerol or pentaerythritol, and subsequentsaponification of the glycerides. Preferred fatty acid components areoptionally hydroxy-substituted, linear C₁₂₋₁₈ fatty acids from the abovelist. As usual in oleochemistry, the fatty acids may be used in the formof technical grade mixtures for the production of the partial estersmentioned.

After their preparation, the partial esters obtainable from theabove-mentioned oligoglycerols and fatty acids may be modified byaddition of ethylene oxide and/or propylene oxide (in random or blockdistribution of the alkylene oxide units). Typically, 1 to 30 molethylene oxide are added per mol partial ester. In the addition ofpropylene oxide, it is important to monitor the solubility in water ofthe modified partial esters obtained which decreases with increasingcontent of propylene oxide groups in the case of partial esters ofhigher oligoglycerols, for example of 10 or more condensed glycerolmolecules, up to 30 propylene oxide units can be added on. In the caseof partial esters of relatively short-chain oligoglycerols, for exampleof 3 to 10 condensed glycerol molecules, generally no more than 1 to 3propylene oxide groups are added on.

The partial esters to be used in accordance with the invention alsoinclude products obtainable by initially reacting the oligoglycerolsused as starting material with ethylene oxide and/or propylene oxide andthen esterifying the product of this reaction with the selected fattyacids. The foregoing observations on partial esters also apply in thiscase.

The optionally ethoxylated and/or propoxylated partial esters to be usedin accordance with the invention are suitable as pigment dispersants fortypical pigment-containing, water-based lacquer dispersions, for examplewater-based dispersions of dispersible polymers, such as acrylates,methacrylates, polyurethanes, polyvinyl acetate, natural and syntheticrubbers and the like. They are particularly suitable for lacquerdispersions based on aqueous alkyd resin dispersions of the typedescribed in detail in Ullmann's Encyclopedia of Industrial Chemistry,Vol. A1, pages 409 to 423. Particularly preferred water-based alkydresin dispersions contain hydroxyl-functional alkyd resins and aredescribed in DE-A 3,318,595, to the overall disclosure of whichreference is hereby made.

In another advantageous embodiment of the invention, the optionallyethoxylated and/or propoxylated partial esters of the above-mentionedtype are used in a quantity of 0.2 to 100% by weight and preferably in aquantity of 0.2 to 10% by weight, based on pigments present in thewater-based lacquer preparations.

The present invention also relates to water-based lacquer dispersions,more particularly based on alkyd resins, containing optionallyethoxylated and/or propoxylated partial esters of the above-describedtype as pigment dispersants.

The invention is illustrated by the following Examples.

EXAMPLE 1

Production of a white test lacquer:

The following components are introduced into a stirred apparatus:

113.0 parts by weight demineralized water 3.5 parts by weightpentaglycerol monolaurate

210.0 parts by weight titanium dioxide 1.0 part by weight foam inhibitor(10% aqueous solution of a commercially available ethoxylatedpolysiloxane).

The following components were added with intensive stirring:

295.0 parts by weight of the water-based alkyd resin preparationaccording to DE-A 3 318 595, Example x;

4.0 parts by weight dimethyl ethanolamine (neutralizing agent for thealkyd resin)

319.9 parts by weight demineralized water

83.6 parts by weight hexamethoxymethyl melamine (curing aid).

EXAMPLE 2

The procedure was as in Example 1, except that the pentaglycerolmonolaurate was replaced by the same quantity of pentaglycerol dioleateas pigment dispersant.

EXAMPLE 3

Production of a black test lacquer:

The following components were mixed in the same way as described inExample 1:

50.0 parts by weight demineralized water

1.8 parts by weight dimethyl ethanolamine

10.7 parts by weight hexamethoxymethyl melamine

40.0 parts by weight carbon black

4.5 parts by weight highly disperse silicon dioxide

45.0 parts by weight barium sulfate

3.5 parts by weight pentaglycerol dioleate.

The following components were added to the resulting mixture:

321.1 parts by weight of the water-based alkyd resin preparationaccording to DE-A 3,318,595, Example 3

4.0 parts by weight dimethyl ethanolamine

407.0 parts by weight demineralized water

106.4 parts by weight hexamethoxymethyl melamine

2.0 parts by weight foam inhibitor (10% aqueous solution of acommercially available ethoxylated polysiloxane).

EXAMPLE 4

The procedure was as in Example 3, except that the pentaglycerolmonolaurate was replaced by pentaglycerol dioleate as pigmentdispersant.

COMPARISON EXAMPLES

Water-based lacquer dispersions were prepared in the same way as inExamples 1 to 4 except that the pentaglycerol monooleate andpentaglycerol dioleate were replaced by the same quantities, based onthe active-substance content, of a commercially available nonionicdispersant preparation (adduct of approx. 10 mol ethylene oxide withnonylphenol; Disponil® 286, a product of Henkel KGaA), an anionicdispersant (Additol® XL 250, a product of Hoechst) and a polyacrylicacid salt according to DE-A 3,318,595, Example 3.

The lacquers obtained as described above were sprayed onto steel platesand stored for 15 minutes at 160° C. The dry film thicknesses werebetween 25 and 40 micrometers. The test results obtained with thelacquer coatings are set out in Tables 1 and 2. The test resultsobtained with the formulations of the Comparison Examples are alsoincluded in the Tables.

                                      TABLE 1                                     __________________________________________________________________________    White lacquer                                                                                      Poly-                                                                         acrylic Example                                                                            Example                                     Dispersant                                                                           Nonionic.sup.1)                                                                      Anionic.sup.2)                                                                       acid salt.sup.3)                                                                      1    2                                           __________________________________________________________________________    Values                                                                        Viscosity,                                                                           975    520    340     530  480                                         mPa · s                                                              Gloss  52%    80%    89%     77%  79%                                         60° ≮                                                      Pendulum                                                                             133    128    131     131  120                                         hardness,                                                                     secs.                                                                         Cross- 2      2      4       2    2                                           hatch                                                                         Impact test                                                                          =40    =40    =40     >40  >40 <70                                     reserve inch                                                                  pound                                                                         Condensation                                                                         240 h  240 h  240 h   240 h                                                                              240 h                                       test   m1/g1  m0/g0  m0/g0   m0/g0                                                                              m0/g0                                       Salt spray                                                                           96 h   96 h   96 h    96 h 96 h                                        test.sup.4)                                                                   MEK test.sup.5)                                                                      140    140    140     160  >170                                        wipes                                                                         Appearance                                                                           1-2 mm Approx. 50%                                                                          Approx. 5 mm                                                                          1-2 mm                                                                             1-2 mm                                      after storage                                                                        serum  serum form-                                                                          serum forma-                                                                          serum                                                                              serum                                       for 30 days                                                                          form-  ation, read-                                                                         tion    form-                                                                              form-                                       at 23° C.                                                                     ation at                                                                             ily homogen-   ation at                                                                           ation at                                           the sur-                                                                             izable         the sur-                                                                           the sur-                                           face                  face face                                        __________________________________________________________________________     .sup.1) Disponil ® 286                                                    .sup.2) Additol XL 250                                                        .sup.3) DE-A 3 318 595, Example 3                                             .sup.4) Acc. to DIN SK 50017, 53209                                           .sup.5) MEK = methyl ethyl ketone                                        

                  TABLE 2                                                         ______________________________________                                        Black lacquer                                                                              Poly-                                                                         acrylic                                                                       acid                                                             Dispersant   salt.sup.1)                                                                             Example 3 Example 4                                    ______________________________________                                        Values                                                                        Viscosity,   850       960       960                                          mPa · s                                                              Gloss,       82%       83%       82%                                          60° ≮                                                      Pendulum     145       145       152                                          hardness,                                                                     secs.                                                                         Cross-hatch  2-3       2         2                                            Impact test  <70       =70       =70                                          reserve inch                                                                  pound                                                                         Condensation 240 h     240 h     240 h                                        test         m0/g0     m0/g0     m0/g0                                        Appearance after                                                                           2-3 mm    2-3 mm    2-3                                          storage for 30                                                                             serum     serum     serum                                        days at 23° C.                                                                      form-     form-     form-                                                     ation     ation     ation                                        ______________________________________                                         .sup.1) DE-A 3 318 595, Example 3                                        

We claim:
 1. The process of dispersing pigment particles in apigment-containing, water-based lacquer dispersion, consistingessentially of adding to said dispersion from about 0.2 to about 100% byweight, based on the weight of said pigment particles, of a partialester of a C₂ -C₁₈ fatty acid with an oligoglycerol obtained bycondensation of about 2 to about 20 moles of glycerol.
 2. The process asin claim 1 wherein said partial ester is ethoxylated or propoxylated. 3.The process as in claim 1 wherein said fatty acid ishydroxy-substituted.
 4. The process as in claim 1 wherein said partialester contains at least one free hydroxyl group in said oligoglycerol.5. The process as in claim 1 wherein said partial ester is obtained bycondensation said fatty acid with an oligoglycerol having of said fattyacid with an oligoglycerol having about 3 to about 10 moles of glycerol.6. The process as in claim 1 wherein said lacquer dispersion consistsessentially of an alkyd resin dispersion.
 7. The process as in claim 6wherein said lacquer dispersion consists essentially of ahydroxyl-functional alkyd resin dispersion.
 8. The process as in claim 1wherein said partial ester is present in an amount of from about 0.2 toabout 10% by weight, based on the weight of said pigment particles. 9.The process as in claim 1 wherein said partial ester contains from about1 to about 30 moles of ethylene oxide or propylene oxide.
 10. Awater-based lacquer dispersion containing pigment particles, and as adispersant for said pigment particles, from about 0.2 to about 100% byweight, based on the weight of said pigment particles, of a partialester of a C₂ -C₁₈ fatty acid with an oligoglycerol, said oligoglycerolobtained by condensation of about 2 to about 20 moles of glycerol.
 11. Alacquer dispersion as in claim 10 wherein said partial ester isethoxylated or propoxylated.
 12. A lacquer dispersion as in claim 10wherein said fatty acid is hydroxy-substituted.
 13. A lacquer dispersionas in claim 10 wherein said partial ester contains at least one freehydroxyl group in said oligoglycerol.
 14. A lacquer dispersion as inclaim 10 wherein said partial ester is obtained by condensation of saidfatty acid with an oligoglycerol having about 3 to about 10 moles ofglycerol.
 15. A lacquer dispersion as in claim 10 wherein said lacquerdispersion consists essentially of an alkyd resin dispersion.
 16. Alacquer dispersion as in claim 15 wherein said lacquer dispersionconsists essentially of a hydroxyl-functional alkyd resin dispersion.17. A lacquer dispersion as in claim 10 wherein said partial ester ispresent in an amount of from about 0.2 to about 10% by weight, based onthe weight of said pigment particles.
 18. A lacquer dispersion as inclaim 10 wherein said partial ester contains from about 1 to about 30moles of ethylene oxide or propylene oxide.